1. Field of Invention
This invention relates to ventricle assist devices useful to aid or replace a damaged heart. More particularly, the present invention pertains to ventricle assist devices which utilize natural muscle tissue as a pumping source.
2. Prior Art
A major challenge in implementation of a convenient ventricular assist therapy remains the development of a power source which is self-sustaining and compact. Typical forms of pumping units include some variation of a mechanical drive unit which utilizes a piston, roller pump, axial impeller, or other mechanical structure for moving pumping fluid through a recirculating drive system. Such a pumping unit must be small in size, capable of alternating and reversible flow, operable on minimal power consumption, consistent and dependable. Without question, the difficulty of mechanically reproducing the simple pumping action of the human heart has been and remains formidable.
It has been well established that a fast-twitching skeletal muscle can be converted into a slow twitching continuous acting muscle, similar to a heart muscle, by chronic stimulation with bursts of electrical pulses. Myoplasty around the natural heart has been done clinically with apparent success in many institutions. Some efforts have also been made to apply skeletal muscle around a blood sac and to use the contraction of the muscle around the blood sac to expel the blood contents in a manner similar to the contraction of a cardiac muscle. The refill cycle occurs by flow under pressure within the vascular system. By attaching this pumping system to the aorta of a weak heart, the pumping action of the muscle powered ventricle assist device can increase circulation to a more effective level. Unfortunately, the pumping capacity of the muscle directly applied to the blood sac is not always sufficient to offer ventricular assist for general applications. Sometimes such a system does not have the power to provide ventricular assist to the left ventricle, which requires greater pumping pressure than the right ventricle.
In addition to these limitations, mortality has been high for patients using this procedure, perhaps in part because these techniques are only applied as a last resort. The myoplasty operation in sick patients requires six hours and requires training of the skeletal muscle for approximately six weeks. To reduce the high mortality rate, selection of patients in deep failure was excluded. Nevertheless, interest in cardiomyoplasty remains high world-wide. Accordingly, what is needed is a form of muscle activated pumping system which supplies greater pressure and which includes additional pumping backup and power source to complement the contraction power offered by the muscle tissue, particularly in the beginning.